This invention relates to improved sewage lift stations, in which, conventionally, sewage passing through sewage pipes is raised to permit it to flow over hills and on to a sewage treatment plant. In the improved sewage lift station, grease is separated from water and solids in sewage, and thereafter transferred separately to remote destinations.
Sewage lift stations, usually comprise rectangular tanks made of precast concrete that are buried below ground A conduit having an inlet end communicates with the interior of the tank and a discharge end at a remote location. A pump, which may be submerged in the tank, pumps sewage from the tank upwardly to a remote destination.
In the tank, any grease in the sewage, being of a lower density than the water in the sewage, rises to the top, forming a separate grease mat layer. The amount of grease in the tank tends to build up over time, since the grease is at the top of the tank, and the pump is usually at the bottom of the tank, resulting in difficulty in evacuating the tank, as well as clogging of the pump and conduit when it is subjected to pumping the grease mat. Periodically, the entire contents of the tank, or the grease along with part of the water, is pumped from the tank.
The prior art discloses various methods and apparatus for separating two immiscible liquids, and also discloses various methods and apparatus for removing one liquid from contact with the other after separation of the liquids into two layers in a separator. For example, in some cases, the lighter liquid is discharged by gravity from the separator through an upper pipe and the heavier liquid is discharged from the separator through a lower pipe. Generally, the methods and apparatus relate to the separation of grease or oil from water.
U.S. Pat. No. 4,400,274 to Protos, describes a gravity separator in which solids are removed prior to separation of the grease and water. In the Protos apparatus, solids and liquids flow by gravity into a first tank. When the tank is filled, grease, which floats to the top of the tank, spills over into a second tank. When the second tank is filled, grease is discharged by gravity from the upper part of the tank, and water is discharged from the bottom part of the tank into a third tank, from whence the water is discharged through gravity flow through a discharge pipe. A vertical screen is present in the first tank to filter grease flowing into the second tank.
U.S. Pat. No. 2,747,736 to Mobley describes a device for removing grease from waste water in a separator, in which grease which floats to the top of the separator is removed by hydrostatic forces. The grease is then stored at a collecting and storage point remote from the separator.
U.S. Pat. No. 5,236,585 to Fink describes a separator in which oil and water are separated. The oil, which floats to the top of the water, flows under gravity to a second separator, where remaining oil is removed, e.g., by filtration. Water is removed from the bottom of the first separator.
Other patents show similar devices. U.S. Pat. No. 4,915,823 to Hall, describes a device for separating oil from water in bilge discharges. After separation, the oil and water are removed through separate discharge pipes. U.S. Pat. No. 4,119,541 to Makaya, discloses a similar arrangement for cleaning up oil spills by separating oil from sea water.
The apparatuses disclosed in the prior art are not used in sewage lift stations in which there is a need to transfer the sewage components to remote destinations, which are located above the lift station, and normally above-ground. In these instance, what is needed is an apparatus which can separate grease from solids and water so as to prevent fouling of the sewage lift pump before transfer of these sewage components to remote destinations above the lift station.